The generation and use of oxidizing agents such as chlorine (through hypochlorous acid), oxygen and ozone for treating and for disinfecting and/or removing undesirable organic materials such as odor and bacteria from waste water, sewage, drinking water environmental air and industrial stack gases is generally known (ref. U.S. Pat. Nos. 4,167,466, 3,342,545 and 3,260,627). The use of ozone for such purposes, however, has been limited, thus far, due to inefficiency in production (ref. U.S. Pat. Nos. 3,883,413 and 3,702,973) and the fact that ozone is biologically toxic and remains chemically active, even in concentrations of less than 1 ppm. As a result, essential organic materials, animal and human life in surrounding areas can be adversely affected by ozone-residues.
The toxic properties of ozone are also particularly troublesome in enclosed areas in which relatively low concentrations (i.e. 0.2-1 ppm) are generated or maintained for long periods, such as in the operation of electrical devices under dry atmospheric conditions, or already present in nature. Such may include, for instance, the prolonged operation of corotrons in xerographic copiers in an office environment or found in airplanes operating above 37,000 feet. Despite its relative instability under moist ambient conditions, the high toxic properties of ozone make it necessary and prudent to further hasten chemical breakdown ##STR1## wherever the rate of generation even slightly exceeds the rate of natural decomposition, so as to maintain a concentration no higher than about 0.25 ppm sea level equivalent, or 0.1 ppm over any period exceeding 4 hours (ref. "Atmospheric Environment"; Vol. 6, pg. 707-714; Pergamon Press 1972; F.A.A. Rules, Federal Register Vol. 45, #14; Jan. 21, 1980).
For air purification and similar purposes, reactants and catalysts such as activated charcoal (ref. U.S. Pat. Nos. 1,961,878 and 3,516,783) silver, platinum and some other metallic oxides have been tried, in the past, with varying degrees of success (ref. U.S. Pat. Nos. 3,352,642 and 3,433,580).
Unfortunately, however, ozone possesses catalytic-inhibiting as well as the above-indicated toxic biological properties, such that normally efficient precious metal catalysts are subject to an early and substantial loss in efficiency under normal practical reaction conditions, and the less expensive metal catalysts found to be too demanding with respect to energy input and generally unable to operate efficiently at high space velocities.
It is an object of the present invention to obtain an ozone-decomposition catalyst which retains a high level of efficiency when exposed to ozone, and is capable of maintaining the catalytic decomposition of ozone on a long-term basis at high space velocities under mild or ambient reaction temperature conditions.
It is a further object of the present invention to develop a method for stabilizing platinum group metal catalysts exposed to ozone or ozone-containing gases.
A still further object is to broaden the utilization of ozone as an oxidizing agent without harm to the environment from residual amounts of ozone-containing gases in the resulting effluent.
It is an additional object of the present invention to develop a method for increasing the efficiency of low temperature catalytic decomposition of ozone by using a platinum group metal such as palladium in combination with a base metal as catalytic components.